Array of tuples throws ClassCastException

[Quafadas]

Compiler version

3.6.3-RC1

Minimized code

val a: Array[(Int, String)] = Array[Int *: String *: EmptyTuple]()

yoshord (<- discord handle, not sure of GitHub handle, apologies) suggest it to be reported after a brief discussion on discord.

https://discord.com/channels/632150470000902164/875868146949554207/1327170970942836777

Here is his Scastie reducing it, although the code above is even terser;

https://scastie.scala-lang.org/EsHwgPChRJqC9Ichpwq4gQ

Output

java.lang.ClassCastException: class [Lscala.Product; cannot be cast to class [Lscala.Tuple2;

Expectation

That this should compile and run.

[bishabosha]

There's a bug in erasure that basically guarantees that generic tuple types are always converted to Product, but then that isn't reconciled with tuple syntax being refined to concrete Tuple2. Maybe for array types we can do better

[mbovel]

@sjrd we need your opinion on this one: would you see a way to fix this without breaking binary compatibility?

[sjrd]

If the fix involves changing erasure, it's probably a no-go.

Is this bug specific to array creation? Maybe we only need to force reduction of the type given to Array.apply?

[mbovel]

Is this bug specific to array creation?

More or less yes, it is specific to seq literals and synthesized classOf instances. I think if we normalize tuple types in these two situations, then we should be good. Would that be an acceptable fix, as it doesn't change the erasure directly?

[sjrd]

Yes, that would be acceptable.